1. Field of the Invention
The present invention relates to a method for manufacturing magnetic paint and a magnetic recording medium. In particular, the present invention relates to a method for manufacturing magnetic recording medium, wherein a dispersion condition during the dispersion through the use of a dispersion device filled in with dispersion media is improved in order to excellently disperse a magnetic powder composed of fine particles adaptable for a higher recording density, so that a magnetic recording medium having excellent surface roughness can be prepared, and to a magnetic recording medium provided through the use of the magnetic paint (hereafter may be referred to as “paint”) prepared by the method.
2. Description of the Related Art
In general, magnetic paint for manufacturing a magnetic recording medium is prepared through the steps of supplying a magnetic paint composition composed of a magnetic powder, a binder, an organic solvent, and other necessary components to a dispersion device in which dispersion media, e.g., glass beads, are filled in a mixing vessel, forcedly agitating the composition together with the dispersion media with an agitator disposed in the mixing vessel, and the like.
On the other hand, with respect to magnetic recording media used for videos, audio equipment, computers, or the like, increases in recording density have even more advanced in recent years. Consequently, the minimum recording unit tends to be miniaturized by reducing the recording wavelength, decreasing the recording track width, and decreasing the recording medium thickness. In order to deal with this, a ferromagnetic metal powder, which is composed of fine particles and which has large magnetic energy, has become used as the magnetic powder.
In the magnetic recording medium, it is important that the magnetic powder has adequate dispersibility in the magnetic paint and the magnetic layer provided has a good surface roughness to attain a high playback output and an excellent S/N ratio of the short-wavelength recording. Therefore, various researches have been carried out on the improvement of the dispersibility of the magnetic powder in the magnetic paint until now. For example, technologies related to materials for dispersion media are described in, e.g., Japanese Unexamined Patent Application Publication No. 60-211637, Japanese Unexamined Patent Application Publication No. 64-57422, and Japanese Unexamined Patent Application Publication No. 1-290122. Technologies related to dispersion conditions, such as the amount of filling of the dispersion media in the dispersion step, are described in, for example, Japanese Unexamined Patent Application Publication No. 2000-339678. Furthermore, there have been proposed the technology for preparing magnetic paint and a magnetic recording medium, each having excellent medium characteristics, by improving the dispersion condition related to the preparation of magnetic paint in Japanese Unexamined Patent Application Publication No. 2001-81406.
Accompanying the reduction in the particle size of the magnetic powder, establishment of an adequate degree of dispersion becomes difficult unless dispersion media having smaller diameters are used. However, since the weight per dispersion medium is decreased with a decrease in the diameter of the medium, an adequate collision force may not be attained, so that a problem of an inadequate degree of dispersion may occur.